1. Field of the Invention
The present invention relates to a fuel injection valve which supplies fuel fed from its top to an internal combustion engine, so called a top feed fuel injection valve, and more particularly to a fuel injection valve having an improved magnetic circuit structure and its manufacturing method.
2. Description of Related Art
An example of a top feed fuel injection valve is shown in JP-A-5-503976. In this fuel injection valve, an injector pipe is composed of a cylindrical fuel connector made of a magnetic material for connecting the injection valve to a fuel delivery pipe, a non magnetic annular member soldered to the bottom end of the cylindrical fuel connector, and a valve body made of a magnetic material soldered to the bottom end of the annular member. The injector pipe is inserted into a cylindrical molded coil, and two yokes are attached to the outside of the molded coil and soldered to the fuel connector and the valve body at their top end and bottom end, respectively. Then, a whole assembled injection valve is molded by resin. Each yoke has a curved plate-like shape and covers a part of the outside of the molded coil.
Some of conventional injection valves have a single cylindrical yoke into which a cylindrical molded coil is inserted. In this structure, the yoke must have an opening larger than the outer diameter of the molded coil, and, accordingly, the yoke opening cannot be directly attached to the outer periphery of the molded coil. So, a magnetic ring has to be inserted between the yoke opening and the injector pipe to form a closed magnetic circuit. This structure requires an additional part, the magnetic ring, and makes its assembling process complex.
The injection valve disclosed in the publication recited above is intended to solve the problem of the conventional injection valves. However, there still remains a problem in its assembling process. That is, the injection pipe has to be inserted into the cylindrical molded coil using a jig to set the injection pipe at a right position in the molded coil, and the yokes have to be positioned at a right place of the outer periphery of the molded coil with help of a jig. This assembling process is inefficient and makes its cost high. Moreover, after the yokes are assembled to the molded coil, a whole assembly has to be molded into one piece by resin, and an annular member to support a sealing member (an O-ring) has to be formed on the upper end portion of the fuel connector. This also makes the assembling process inefficient and makes the assembling cost high.